Unexamined Japanese Patent Application Kokai Publication No. 2002-171023 (Patent Literature 1) describes a package (laser module) that enables computation of the variation in the intensity and wavelength of emitted laser light.
The package is equipped with multiple semiconductor lasers (laser diodes) having different wavelengths of emitted laser light. Light is emitted from each semiconductor laser, and after passing through a collimating lens, rear light is split into a forward direction and a 90° reflected direction by a beam splitter. The package, using a photodetector, then enables measurement of the intensity of the split light by sensing the light split into the 90° reflected direction. Thus, the package enables computation of the intensity of laser light emitted from the semiconductor lasers on the basis of the measured intensity of the split light.
Furthermore, in the package (laser module) described in Patent Literature 1, the light in the forward direction that was split by the beam splitter is sensed with a photodetector after being transmitted through an etalon filter having a wavelength-dependent transmittance, thus enabling measurement of the intensity of the transmitted light transmitted through the etalon filter. Thus, the package enables computation of the variation in the wavelength of laser light emitted from the semiconductor lasers. Specifically, the package computes the transmission coefficient, being the ratio of the measured intensity for the transmitted light transmitted through the etalon filter versus the measured intensity of the light that was split into the 90° reflected direction. By comparing the computed transmission coefficient to the transmittance unique to (characteristic of) the etalon filter, the package enables computation of the variation in the wavelength of the laser light emitted from the semiconductor lasers.
In this way, the package (laser module) described in Patent Literature 1 enables computation of the variation in the intensity and wavelength of laser light emitted from semiconductor lasers by causing the rear light to be emitted from semiconductor lasers, transmitted through a collimating lens, and split with a beam splitter.
As described above, the package described in Patent Literature 1 includes a beam splitter that splits light in order to compute the variation in the intensity and wavelength of laser light emitted from semiconductor lasers. Since the beam splitter needs to split all laser light of differing wavelengths emitted from the semiconductor lasers, the beam splitter is larger in scale compared to the semiconductor lasers and the photodetectors. Consequently, there has been a problem in that the package (laser module) described in Patent Literature 1 is difficult to miniaturize.